A passenger vehicle may include a heat pump to warm and cool a passenger cabin. In some examples, the heat pump may heat the passenger cabin by first transferring heat from a refrigerant to engine coolant. The engine coolant is then directed to a heater core in the passenger cabin where passenger cabin air passes over the heater core to heat the passenger cabin. However, if an exterior heat exchanger of the heat pump experiences icing, the passenger cabin may not reach a desired temperature because of inefficient heat pump operation. The exterior heat exchanger may be de-iced by passing warm refrigerant through the heat exchanger. One way to warm the refrigerant is to operate the heat pump in cooling mode, where the exterior heat exchanger operates as a condenser. However, operating the heat pump in a cooling mode removes heat from the passenger cabin at a time when the driver may require heat. As a result, passenger cabin temperature may be reduced or it may not reach a desired temperature in a desired amount of time.
The inventor herein has recognized the above-mentioned disadvantages and has developed a method for thawing a vehicle's exterior heat exchanger, comprising: increasing an opening amount of an expansion valve located along a passage between a compressor and an exterior heat exchanger in response to exterior heat exchanger icing; and activating a first positive temperature coefficient (PTC) heater in response to the exterior heat exchanger icing, the PTC heater in thermal communication with refrigerant passing through the expansion valve.
By heating refrigerant of a vehicle's heat pump using a PTC heater, it may be possible to provide the technical result of more rapidly de-icing a vehicle's exterior heat exchanger while not removing heat from the passenger cabin. Consequently, it may be possible to increase passenger cabin heat in less time. For example, the vehicle's heat pump may enter a de-icing mode where an expansion valve supplying refrigerant to the exterior heat exchanger is nearly fully open, while at the same time, PTC heaters increase refrigerant temperature further so that exterior heat exchanger de-icing may complete sooner. The expansion valve is adjusted to maximize heat transfer to the exterior heat exchanger from the compressor and the PTC heaters. In this way, exterior heat exchanger de-icing may be expedited without removing heat from the passenger cabin.
The present description may provide several advantages. For example, the approach may improve passenger cabin heating of electric and hybrid vehicles. Further, the approach may improve heat pump efficiency. Further still, the approach may improve a vehicle's electric propulsion range when the heat pump is activated by using energy from regenerative braking to defrost the exterior heat exchanger.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.